However, if one considers the figure below, there do seem to be number of slightly different results, depending on the method used. All seem to produce 5-95% ranges of about 1-4K, but the median seems to vary from just below 2K, to just above 2K.

Credit: Lewis & Grunwald (2017)

Roughly speaking, this result seems broadly consistent with the IPCC range of 1.5-4.5K (although that might be a 17-83%, rather than a 5-95%, range), with a slight shift to lower values and a lower median than might be expected. A few general comments, though. Unless clouds happen to provide quite a strong negative forcing, there are robust physical arguments as to why ECS > 2K. There are also indications that the cloud feedback is probably positive. There are also reasons to be slightly cautious about some of these Bayesian estimates of climate sensitivity, which we discussed in some more detail in this post (in fact the priors shown in Figure 3 in the paper seem to highlight what we discussed about Nic Lewis’s priors).

However, I do think that this new paper is a nice extension of the work Nic Lewis has done before. What would be nice would be to maybe include more physics so as to exclude regions of parameter space that we regard virtually impossible (for example, ECS values below 1K). My suspicion is that doing so would shift the distribution to slightly higher values and would make the result even more consistent with the IPCC estimates.

But you don’t really need it for observational evidence or paleo proxy data.

I would disagree. Physics provides constraints applicable to the real world. Data without some kind of model is largely useless. If your data analysis gives a result that is physically implausible, then you really should try to incorporate something into your analysis that precludes that outcome. This isn’t, however, a criticism of the Lewis & Grunwald paper; I think it’s a nice piece of research. However, I think that if they were to incorporate some kind of physics into their analysis (by, for example, incorporating that an ECS < 1K is very unlikely into their prior) I think there result would become even more consistent with the standard IPC result.

By blotting base 2 log of CO2 vs temp (s)he shows “temperature increases linearly per doubling of CO2 (Fig. 1); the trend line has a slope of 2.39, meaning that the global mean temperature increases by 2.39 °C for each doubling of CO2 concentration, with a 95% confidence interval of 2.24 – 2.55 °C.” – which sounds about right for TCR.

lerpo,
That sounds a bit too high and a bit too certain. One reason – I think – is because the likely change in anthropogenic forcing is slightly higher than that due to CO2 alone. Hence your calculation ignores some of the change in external forcing.

Steve, allow Eli to do the zeroth order argument. Solar irradiance has varied ~1-2 parts in 1300 over the satellite era by direct measurement. The global temperature anomaly increase has been much higher on any basis

Paulskio asks “How do you get an ECS estimate from instrumental or proxy temperature data without a prior physical model?”

You can estimate the temperature difference between various doublings of CO2 using proxy data.

For example, you use proxy data to estimate the temperature at 180 ppm of CO2 in the atmosphere, than at 360 ppm. That gives you a TCR estimate. You could wait 500 or 1000 years, and measure the temperature using proxy data after 360 to allow equilibrium and measure the temp using proxy data and get an estimate for ECS.

Do this for 190 and 380, 200 and 400, and so on.

Of course, I am not a climate scientist – just a layperson. But I don’t see why this wouldn’t give an estimate using paleo data.

Soon we will be able to do the same thing with instrument data.

We have temperature data for 280 ppm and in a few decades should hit 560 ppm and can then measure TCR. Obviously we have to wait for whatever time period we think it takes to reach equilibrium – but we could then directly measure ECS as well.

We can then do that for doublings from 290 ppm, 300 ppm and so forth.

I am no climate scientist – but why cannot this be done? No physics required.

I think Eli is simply suggesting that physics also constrains how sensitive our climate can be and largely precludes the possibility of the observed warming being a consequence of small changes in solar flux, or cosmic rays.

What would be nice would be to maybe include more physics so as to exclude regions of parameter space that we regard virtually impossible (for example, ECS values below 1K). My suspicion is that doing so would shift the distribution to slightly higher values and would make the result even more consistent with the IPCC estimates.

Closer to ~3C, I suspect. I don’t share your benign view of Nic Lewis and his oeuvre at all, ATTP. Not at all.

For example, you use proxy data to estimate the temperature at 180 ppm of CO2 in the atmosphere, than at 360 ppm. That gives you a TCR estimate.

Why not estimate an ECS relationship using the LGM to pre-industrial change for CO2 (180ppm to 280ppm) and temperature (about 5K) then apply that statistical relationship to a doubling from 280ppm? So, 5K divided by 100ppm = 0.05K per 1ppm. That means ECS for a doubling to 560ppm would be 14K.

Do we believe that 14K could be realistic? No, because physics. For one thing CO2 forcing is found to have a roughly logarithmic relationship with concentration, hence the last 100ppm from 460 to 560ppm is actually expected to be considerably weaker than the 100ppm from 180 to 280ppm.

I don’t share your benign view of Nic Lewis and his oeuvre at all, ATTP. Not at all.

Benefit of the doubt. I may be being too generous. What I will say, though, is that there are a number of recent papers that have looked at the instrumental climate sensitivity estimates that Nic Lewis favours. This new paper appears to not cite any of them. Given that Nic Lewis has writtenblogpostsabout most of them, he can’t exactly claim to not have been aware of them. This is pretty poor. You’re meant to cite the relevant literature, not only the papers that support what you’re presenting.

RickA: “I am no climate scientist – but why cannot this be done? No physics required.”

Well, note that Paulski0 said “a prior physical model”, in response to your comment about physics and models. You’ve already assumed that there is a relationship between CO2 and temperature. Is that linear? Log-linear? You’ve also assumed that you need to wait 500 to 1000 years to get equilibrium sensitivity. And that you can get transient sensitivity over some shorter (unspecified) time frame. You’ve also assumed that proxy data has some relationship to temperature.

Sounds to me like you already have some idea of what sort of models will be used to analyze the observations. Are you absolutely sure that none of these have any physical (or physics) characteristics at all?

The definition is what I am using. ECS is defined as the temperature rise from doubling of CO2. Sure you can linearly project from 100 ppm to a full doubling – but that is probably wrong for the reasons you pointed out. Why assume a linear relationship when you can just measure at doubling points?

Of course, you can do what you want – but I cannot see why you cannot also use paleo data to determine delta T at doubling points, or use instrumental data to determine delta T at doubling points.

The actual observations have the physics inherent in them – do they not?

Just observe and apply the definition – no physics required (other than what is already buried in the actual observations).

Rick,
Without the physics, though, you would have no idea as to the significance of a doubling. The significance is that every doubling of atmospheric CO2 produces – approximately – the same change in radiative forcing.

“I think Eli is simply suggesting that physics also constrains how sensitive our climate can be and largely precludes the possibility of the observed warming being a consequence of small changes in solar flux, or cosmic rays.”

The comparison of observations with hypothetical ECS ranges allows the framework of the questions.

At what time would such equilibrium occur?
What processes would differ at such time?
At what rate would these processes exert influence?

Because the observed rate is relatively constant, it would appear that ECS processes, if they exist, would have to be multi-centennial rather than what the multi-decadal history bears out.
As we know, the heat capacity of the oceans can become a very large reservoir of energy.
OHC could provide such a duration of change.

However, if heat becomes diffused through out the oceans, it will emerge very slowly, continuing to buffer and smooth out imbalances.

Because the observed rate is relatively constant, it would appear that ECS processes, if they exist, would have to be multi-centennial rather than what the multi-decadal history bears out.

The ECS will probably take centuries to fully realise. However, as your figure shows, the rate at which we warm largely depends on the rate at which we change the radiative forcing. In the next few decades we could produce a change in radiative forcing that is comparable to the change we’ve experienced since the mid-1800s. Therefore, the rate at which we will warm in the coming decades does not have to be similar to the rate at which we’ve been warming and could well be considerably faster if we continue to increase our emissions.

However, if heat becomes diffused through out the oceans, it will emerge very slowly, continuing to buffer and smooth out imbalances.

In some sense, yes, but if we can rapidly diffuse energy to the deep ocean, the TRC-to-ECS ratio will be smaller than if the diffusion rate is slow. This is one reason to be suspicious of the Nic Lewis’s TCR and ECS best estimates. They probably both can’t be realistic because that would imply a large TCR-to-ECS ratio.

Nic just uses HadCRUT4 and I didn’t see a mention of how it is non-global and has blending issues which mean it isn’t comparable with IPCC climate model estimates.

Climate models suggest a ~24% increase to the energy budget estimates is in order if you want global air temperature. Or you could use Berkeley, which has better coverage and seems to have less of a blending effect due to how it handles sea ice changes. That gives ~29% higher ECS than HadCRUT4 using the “preferred period” of 1859-1882 through 1995-2011. Not sure how it would affect Nic’s results after the Bayesian mixing with paleo. It would also be helpful if they’d tested their techniques on CMIP5 simulations when we know the answer.

… and in that time we will start to see slow feedbacks coming to bear, so the final equilibrium response will be much larger, perhaps up to double that implied by the ECS.

It is often (universally?) ignored that ECS is only a theoretical construct, not a physically directly measurable quantity, and that it is by definition less than the equilibrium response to an increased CO2 level.

vtg,
Indeed, the ECS only takes fast feedbacks into account and, hence, the warming that we will actually see (for a given, long-term, atmospheric CO2 concentration) will likely be higher than the ECS.

MarkR,
Thanks. Yes, those are good points. I would expect that if they had taken those factors into account their median estimate would have increased slightly. Once again, it seems hard to justify an ECS below 2K.

The correlation between the 91 models in CMIP5 RCP4.5 runs that have published ECS values for 1861-2005 (last five years averaged minus the 1861-99 average) is -0.01. If the forcing and its variations within the models is consistent with that behind observations, then observations will tell us nothing about ECS.

If the historical period within the models is extended to 2016 (we are on RCP4.5, which is lower than the real world but it won’t matter much within this interval), then the correlation with model ESC is 0.18. Positive, but tells us very little. If the single year of 2016 is sampled, then the correlation rises to 0.25, still not enough to matter much.

Whereas by 2095, the correlation between total warming and ECS is 0.77. Correlation over the period 2006 to 2095 is 0.81. The best way to estimate climate sensitivity is to be there, not here and now.

The low historical correlation is due to decades with negative forcing (the 1950s and 1960s), counterbalancing the decades with strong forcing (1970s and 1980s), with the period around Pinatubo being neutral. Observations therefore are not likely to usefully constrain ECS in any Bayesian assessment because the terms contributing to positive atmospheric feedback cancel each other out. Even if this is somewhat exaggerated in the models compared to obs, updating these numbers in a Bayesian analysis can tell us very little.

To claim that observations can tell us something about ECS, we first have to see whether it is a meaningful test by using the best info to hand – model output – and show that the models demonstrate a relationship within the window being examined. These numbers suggest that isn’t the case.

I wonder if the IPCC regrets using it, because it cannot be measured directly and lends itself to fighting over when equilibrium has been reached. Also, during the wait for equilibrium, any changes to the forcings and a whole new argument will erupt (like a volcano).

Maybe we should ditch it and just rely on TCR.

At least we can directly measure TCR by just waiting until we hit 560 ppm, measuring the global mean temperature and subtract the global mean temperature from when we where at 280 ppm.

“Roughly speaking, this result seems broadly consistent with the IPCC range of 1.5-4.5K (although that might be a 17-83%, rather than a 5-95%, range),”
Eyeballing the graphs roughly there appears to be little correlation with the Lewis best estimate way below the IPCC estimate.
BBD prefers 3.0 Lewis would be lucky to be 2.0.
–
“What would be nice would be to maybe include more physics so as to exclude regions of parameter space that we regard virtually impossible (for example, ECS values below 1K).”
If the physics is right why do we have to include “more” physics? Surely impossible results will be excluded by the physics we have, if it is right in the first place, not more of it.

angech,
What do you mean? It probably isn’t easy, even though there are some simple methods one can use to produce estimates. The problem, though, is that these simple methods may ignore factors that could end up being quite important. This isn’t all that unusual a situation.

That’s rather problematic. Because if it is true you either read a lot about ECS without understanding it, *or* deliberately misrepresented it, given that your initial assertion in this thread turned out not to be supportable.

Anyway, having read so much, you’ll know the definition of TCR (you *do* know that, right?), and you’ll be able to point out the problems with your bald assertion on its measurement. Suggestions just for starters: 1. look at the news from Bali; 2. Look at the rate of increase at 280 and 560ppm; 3. Physics.

That’s rather problematic. Because if it is true you either read a lot about ECS without understanding it, *or* deliberately misrepresented it

Elements of both. RickA has a long and problematic history of this (see eg. Greg Laden’s blog). RickA has had his various misunderstandings explained many, many times, so we are now deep in the realm of bad faith peddling here.

No adjustments for volcanoes are required, just wait until CO2 doubling (560 ppm), measure the global mean temperature and subtract the global mean temperature from 280 ppm and there you have it – TCR. No physics required, no models required.

You just directly measure it.

Of course, the doubling from 280 to 560 gives you only one data point.

You could also measure the temperature at 290 and 580 and get a second data point.

You could measure the temperature at 300 and 600 and get a third data point.

Why, over time, you could actually build up a whole database of actual TCR measurements and study them, much like we do actual temperatures.

Yes – from your second link, in the Figure 9.1 description it says “The �transient climate response�, TCR, is the temperature change at the time of CO2 doubling and the �equilibrium climate sensitivity�, T2x, is the temperature change after the system has reached a new equilibrium for doubled CO2, i.e., after the �additional warming commitment� has been realised.”

Sorry for the funny � characters – they are in your link.

Also, from the technical summary of WG1 of TAR is this:

“Used for the first time in this IPCC report is the Transient Climate Response (TCR). The TCR is defined as the globally averaged surface air temperature change, at the time of doubling of CO2, in a 1%/yr CO2-increase experiment.”

So you can estimate TCR with a climate model and a 1%/yr experiment.

But you do not deny that you can also actually measure TCR by measuring the globally averaged surface air temperature change at the time of doubling of CO2 – do you?

Actual measurements are better than estimates – wouldn’t you agree?

The only reason we rely so heavily on climate models is we are waiting around for a CO2 doubling to occur. Once we have that doubling, we will switch from estimates of TCR to actual measurements of TCR (at least that is what I expect to occur).

I certainly expect scientists to obtain actual measurements of TCR once that is possible, and compare them to the estimates of TCR obtained from the 1%/yr model experiments and study the results. Why, climate scientists might actually use this data to improve climate models.

That is how science works.

The actual measured TCR will be used to check the estimates of TCR.

I hope you do not disagree with this, as this is a very normal scientific process.

Okay, I’m not entirely sure what the dispute is, but I think that VTG’s point is that – formally – both TCR and ECS are model metrics based on simulations in which atmospheric CO2 is increased at 1% per year until it doubles or, in some cases, quadrupoles. In reality, determining both the TCR and ECS via observations is an approximation of these metrics.

Rick,
VTG has already made the key points. The TCR is formally something we estimate from models. We can use observations to try and infer these metrics, but the real system is very complex and so we can’t actually directly measure something like the TCR. For example, even if we did wait until atmospheric CO2 had doubled, we still wouldn’t be able to say with certainty that some internally-driven process hadn’t suppressed forced warming in such a way that the observed temperature change was smaller than it would otherwise be. Also, it’s really related to a change in forcing equivalent to a doubling of atmospheric CO2, not simply to doubling atmospheric CO2. We can’t precisely determine the change in radiative forcing. etc.

The temperature change at any time during a climate change integration depends on the competing effects of all of the processes that affect energy input, output, and storage in the ocean. In particular, the global mean temperature change which occurs at the time of CO2 doubling for the specific case of a 1%/yr increase of CO2 is termed the transient climate response (TCR) of the system. This temperature change, indicated in Figure 9.1, integrates all processes operating in the system, including the strength of the feedbacks and the rate of heat storage in the ocean, to give a straightforward measure of model response to a change in forcing.

You could just take the TCR definition as given and apply without knowledge of the physics, as you can apply any equation/algorithm without understanding how it works. But you’re ultimately using something which has been defined through physics, and is only relevant because of physics.

But if you’re going to operate on a zero-knowledge basis you need to apply the definition precisely. It’s not just about the change at CO2 doubling, it’s the change after 70 years of 1%/year CO2 increase from a standing start (which results in 2xCO2 at 70 years), all other factors remaining constant. The reality is it’s already been considerably longer than 70 years since we left 280ppm and many other factors have refused to remain constant (e.g. methane, aerosols, ozone).

If you do a 1%/yr model experiment, with a supervolcano scenerio, and the temperature difference between 280 and 560 (as an example) is negative (i.e. we cooled over that period due to the eruption), would not TCR be negative?

Or, say you do a model experiment in the far future, as we are entering the next glacial period. Say CO2 drops from 560 to 280 and the temperature drops as well. Is TCR negative?

I predict that climate scientists will call the temperature change between 280 ppm and 560 ppm an “actual measurement of TCR”. Mark my words and lets check back when this occurs.

I predict that climate scientists will use actual measurements of TCR to check their model experiments. Mark my words and lets check back once CO2 doublings with instrumental temperature data occur.

If you do a 1%/yr model experiment, with a supervolcano scenerio, and the temperature difference between 280 and 560 (as an example) is negative (i.e. we cooled over that period due to the eruption), would not TCR be negative?

No, because – by definition – the TCR is the temperature change (at the point at which atmospheric CO2 doubles) in a model in which the only change is atmospheric CO2 and in which this increases at 1% per year. For completeness, it’s also something like the difference between the temperature at the beginning and the temperature averaged over a 20 year period between years 60 and 80 (I think). If you change anything else, then you’re no longer determing the TCR.

So, when the IPCC refers to the TCR being related to a doubling of atmospheric CO2, they’re referring to models in which this is the only thing that changes. In the real world, this is not the case. When we’ve doubled atmospheric CO2 the change in radiative forcing may not be equivalent to a doubling of atmospheric CO2 because there are other factors that can also influence the change in external forcing.

if you guys want to pretend that in the real world the world cannot cool as CO2 doubles (supervolcano)

No, this is not what is being suggested. If we had (which I hope we don’t) some kind of supervolcano, then it could cause the world to cool. The point is that the TCR is essentially defined in terms of a scenario in which the only change is atmospheric CO2. In the real world, this is not what happens. Therefore, defining the TCR as the temperature change when atmospheric CO2 has doubled is not consistent with the formal definition, because – in the real world – it is not only atmospheric CO2 that is changing.

In a sense you need to consider the net change in external forcing (all GHGs, volcanoes, Solar) if you want to estimate the TCR from observations (and even this is not quite the same as a simulation in which atmospheric CO2 is increased at 1% per year). If there were lots of volcanic activity, then it would act to reduce the net change in radiative forcing and the corresponding temperature change would probably be smaller than if there was less volcanic activity. This does not mean that the TCR itself is lower.

Have you ever wondered what the point of your version of TCR and ECS is?

Really, what is the point?

I really don’t get it.

It’s to relate the temperature change to a change in external forcing. The models use CO2 only, but in the real world it doesn’t have to be only CO2. As VTG has pointed out, the real world will still not be entirely the same as a model simulation, but these metrics still give us an indication of how much we would warm (either transient, or equilibrium) if we were to have a change in radiative forcing equivalent to a doubling of atmospheric CO2.

In case anyone is puzzled by this exchange, the point is for RickA to introduce the idea that TCR cannot be known until doubling. This serves as the basis for his position that we don’t know enough* to take action on emissions and should therefore leave well alone until we can ‘observe’ TCR at 560ppm. Then – and only then – can we decide whether or not to have a think about policy.

*So much uncertainty – except about the fact that S is right at the bottom of the range, of course.

I am not against adopting a policy now. As you know I advocate increasing the electricity we produce from nuclear from 20% to 40, 60 or even 80%.

I am only one vote – so I cannot really influence policy, as such.

But yes – model experiments can produce lots of different TCR’s.

You can run them with different amounts of CO2 being emitted or different forcings from volcanos or solar or ocean currents or particles from space or what have you. So you end up with a wide range of TCR’s.

But yes – my point is that once we have a temperature change due to a CO2 doubling – that has to mean something. So I would recommend looking at it. Maybe it will show the models are perfect, maybe it will show the models are running to warm. But I really don’t think climate scientists will ignore the actual measured temperature change from a CO2 doubling.

You can run them with different amounts of CO2 being emitted or different forcings from volcanos or solar or ocean currents or particles from space or what have you. So you end up with a wide range of TCR’s.

No, you would end up with a wide range of temperature changes, not a wide range of TCRs. The TCR is – by definition – the temperature change associated with a change in forcing equivalent to a doubling of atmospheric CO2. In particular, it is a model metric in which the model is run with the only change being atmospheric CO2. If you change anything else, then the resulting temperature change is not the TCR.

Another discussion of Watt’s on the far side of the decimal point for Climate Sensitivity. (Groundhog day, rickA needs to learn the piano)

The aspect of this I always find confusing is whether a low climate sensitivity means that somehow the energy imbalance is less than expected so that the temperature required to re-balance the W/m2 is lower.

Or is it that the heat capacity of the climate system is higher so it requires longer to aquire enough Joules to raise the temperature to the energy balance point.

In the second case a low climate sensitivity would seem to be a bad thing. It may take longer to reach equilibrium temperature, but the system has absorbed a lot more energy in the process. It is difficult to see how the amount of energy, is not a factor in the severity of impacts.

I think it could be either depending on the definition of climate sensitivity. As you imply, a low TCR with high ECS has the potential danger of lulling us into a false sense of security. Equally, it gives more time for adaptation.

The instantaneous doubling of CO2 was deemed a bit unrealistic, as we are gradually raising the amount of CO2 in the atmosphere over time.

They picked 1% and 70 years, because if you compound 1% over 70 years you double your starting value (in other words you go from 280 to 560 ppm).

It was an attempt to make a model which was more like the real world.

That is why the real world temperature change from a doubling of CO2 actually means something.

But as everybody here knows, I am not a climate scientist or really any type of scientist.

I find the push-back against observing an actual temperature change from CO2 doubling very interesting.

I would still like to know what to call the temperature change from a CO2 doubling and do you think climate scientists will think this an important observation and use it to validate their climate models?

In my opinion, how could they not find it useful – but want to here your opinions.

That is why the real world temperature change from a doubling of CO2 actually means something.

Except it won’t be representative of the TCR unless all that has changed is atmospheric CO2. Since this will almost certainly not be the case, simply considering the doubling of atmospheric CO2 is not an appropriate way in which to observationally estimate the TCR.

The temperature the system reaches is determined by the energy imbalance, the positive forcings, in W/m2.

If Agung blows big (I don’t know how much it has input into the stratosphere at this point) then if TCR is low there will only be a small brief ‘hiatus’ in warming from the positive imbalance from CO2/water vapour.
If TCR is large there will be a short, but larger pause, or even cooling, before rapid warming catches up with the positive forcing.

Is this correct?

Only those factors that can directly affect the size and sign of the forcing determine the temperature required to match W/m2 in with W/m2 out.

Climate sensitivity is a resultant of those factors, and the timescales required to reach equilibrium, not a cause.

I find the push-back against observing an actual temperature change from CO2 doubling very interesting.

The push back is entirely in your head.

*All* observations of the climate system are interesting. They *all* add to our understanding of the future climate, and it’s impact on the natural world and human society. A massively wide diversity of such measurements, from fossilised leaf stomata through to satellite accelerometry can be used. No one observation is the holy grail.

Short term (TCR), medium term (ECS) and long term (ESS) sensitivity are just some of the metrics relevant to informing this view.

None of these can be directly measured, only inferred through the use of models.

That is why measuring the actual temperature change from a doubling of CO2, which integrates all the forcing between those two points in time, seems useful to me.

We live in the real world and we need to study the real world – not some idealized model world in which nothing we learn can ever be applied to the real world (at least based on what I have been told in this thread).

Of what use are climate models to policymakers if they cannot tell us anything useful if Agung blows.

Do you understand that the 1%/yr model experiment, which is run over 70 years, is just another way to say look at the temperature change from a doubling of CO2. Because the CO2 doubles over 70 years if increased from its starting value 1% per year. So the climate model experiments are looking at the temperature change from a doubling of CO2. You get that right?

Since in the real world we can never ensure that nothing changes except CO2 – what is the use of TCR? Or ECS?

The models can never be tied back to the real world.

What a waste of time and money.

But we can estimate the actual change in radiative forcing and then relate that to the equivalent change in atmospheric CO2, to then produce an estimate of the TCR/ECS. This is essentially what Nic Lewis’s work does. The point, though, is that it is not as simple as “wait till atmospheric CO2 doubles”.

But yes – I find Nic Lewis’s work very interesting (ECS of about 1.8C).

But you are mysteriously uninterested in the majority of other studies which show that ECS is unlikely to be so low. Instead, you fixate on an outlier and refuse to acknowledge that this is what you are doing.

Since in the real world we can never ensure that nothing changes except CO2 – what is the use of TCR? Or ECS?

The models can never be tied back to the real world.

What a waste of time and money.

And off you go with the ‘we don’t know enough’ rhetoric again. We’ll be back to the pretense that more nuclear in the US is a serious alternative to global scale decarbonisation policies next.

They model that by looking at the doubling of CO2 over 70 years, with a 1% increase of CO2 each year. It is must one doubling experiment – I am sure you could do many other doubling experiments. The important thing is the doubling (because it is in the definition).

All I am saying is in the real world, we can also observe the actual temperature change from a doubling of CO2 (which will take more than 70 years, but the definition is doubling – not the time it takes to double).

I call that an actual measurement of TCR.

You all want to disagree, which is your right – and instead say TCR is only defined by the model experiment the IPCC uses to model the real world (1% increase over 70 years). Since this will probably not happen in the real world – especially the keeping all other forcings constant part – what is the point of being so hidebound with the model definition?

I think actual measurements of the temperature difference between various CO2 doubling will make for useful observations. I think even verytallguy would agree – measure everything and it can all be useful.

Anyway – that is my layperson point of view.

Perhaps a real climate scientist is lurking and can offer some real world insight into what use TCR and ECS have if they only have meaning inside climate models.

@-RickA
“I find the push-back against observing an actual temperature change from CO2 doubling very interesting. …
In my opinion, how could they not find it useful – but want to here your opinions.”

I think they would find it very useful.

If only they could get the funding to construct an exact duplicate of the Earth as it was in 1850 and then remove all further human influence but arrange for CO2 to double in the atmospheric percentage over 70 years (allowing for different sink takeup rates), they would have undoubtedly tried it by now.
Our contract with Magrathea would have been submitted back in the 1960 I suspect.

Unfortunately without that level of funding, and planet making ability, science has had to make do with using the best understanding we have of the physics and chemistry of the Earth we can observe and use that understanding to guide what we need to measure. Luckily the computability of the material universe makes it possible to use Turing machines to create mathematically isomorphic simulations of what is observable.

Of course climate scientists will use actual real world models to check the observations. At least I hope they do – otherwise you will be completely untethered from reality.
See Victor at http://variable-variability.blogspot.co.uk/ for a lot more on that issue.

No, it is defined in a scenario in which the only change is a doubling of atmospheric CO2. It’s not simply any scenario in which atmospheric CO2 doubles. The approximate equivalent in the real world would be a scenario in which the net change in radiative forcing is equivalent to a doubling of atmospheric CO2.

Do you understand that the 1%/yr model experiment, which is run over 70 years, is just another way to say look at the temperature change from a doubling of CO2. Because the CO2 doubles over 70 years if increased from its starting value 1% per year. So the climate model experiments are looking at the temperature change from a doubling of CO2. You get that right?

Yes, the TCR is a measure of the dynamic response of the climate system over a time period of 70 years. It cannot be measured directly in the real world. You get that, right?

Now…

I think actual measurements of the temperature difference between various CO2 doubling will make for useful observations. I think even verytallguy would agree – measure everything and it can all be useful.

You might try reading what I write. Upthread:

*All* observations of the climate system are interesting. They *all* add to our understanding of the future climate, and it’s impact on the natural world and human society. A massively wide diversity of such measurements, from fossilised leaf stomata through to satellite accelerometry can be used. No one observation is the holy grail.

Short term (TCR), medium term (ECS) and long term (ESS) sensitivity are just some of the metrics relevant to informing this view.

None of these can be directly measured, only inferred through the use of models.

In my opinion, the only way for the globe to decarbonize is through nuclear. Renewables just burn more fossil fuels, because we don’t have grid scale power storage yet.

Thank you for your opinion but the view of energy experts is that it is technically infeasible to scale nuclear to decarbonise global electricity generation. It could, and arguably should be part of a future energy mix also incorporating solar and wind and other low-carbon generation technologies.

Knowing you as I do, it is impossible any longer to take your views on energy at face value. They are simply rhetorical caltrops thrown in the way of serious discussion about doing anything at all.

“I don’t think I am redefining what TCR means.
The IPCC says it is the temperature change from a doubling of CO2.”

You might want to listen to the people here who have tried to explain this to you. The IPCC refers to the TCR in an idealized experiment where only CO2 is changed, and where various rapid feedbacks are taken into account. *You* want to look at the temperature change after we’ve reached a doubling of CO2 in a non-idealized real-life situation where other forcings may contribute positive or negative during this time. Stuff like a reduced or increased solar intensity, big volcanic eruptions, increased or decreased particulate emissions into the higher parts of the atmosphere, etc.

Now, if it were so simple to say that to take the increase in temperature after a doubling of CO2 is enough to determine TCR (your ‘definition’), we can also do it with less than a doubling. We don’t need to wait very long. But these weird and strange experts in the field (Isaac Held and Mike Winton) somehow suggest that can’t be done. Why do they think so? Because there are other factors to consider in relating temperature change to TCR. Factors that you just threw out by stating you don’t need a physical model to determine TCR. Clearly, you do need such a model!

I thinl I’ll wait until there is 4X CO2 or maybe 8X or even 16X, fudge TCR, ECS and ESS anyways. It’s not rear until I see it in my real view mirror.

By the time CO2 reaches 560 ppmv I’ll only be 128 years old, but by then, I’ll know for sure.

Maybe I’ll wait until all the ice sheets are completely gone, by then I’ll only be 1,280 years old.

A form of a formal fallacy known as circular reasoning, (1) temporally circular since the arguer is most likely to be dead before the required threshold is met, and (2) current data and future data between now and then, as it continues to behave as it has, will show, at a much earlier time, that a 2X CO2 will lead to some multiple of real time temperature increase (uncertainty will only decrease with time).

Applying Berkeley Land+Ocean up to 2007-2016 using the Otto at al. method and NOAA AGGI numbers for updated forcing I get TCR/TCS = 1.67K.

Furthermore, the 2007-2016 stretch still samples mostly in the “hiatus” period. Assuming a plausible Berkeley 2017 anomaly of 0.84K, even zero net warming from 2017 to 2024 (I.e. all anomalies set to 0.84) and forcing increasing in-line with the past decade, the TCR/TCS keeps incrementing in every ten year window and hits around 1.8K for 2015-2024.

Also interesting developments in energy imbalances. According to the latest CERES-EBAF net toa flux data calibrated to Argo the 2007-2016 average imbalance was 0.8W/m2. Unless 2017 reverses the tendency for post-El Nino years to have higher net fluxes than during El Nino, the 2008-2017 average should be up at around 0.9W/m2. That would indicate an EffCS of about 2.6K using Otto at al. setup.

“Perhaps a real climate scientist is lurking and can offer some real world insight into what use TCR and ECS have if they only have meaning inside climate models.”

I explained above why we can’t use historical data to narrow the range of climate sensitivity (or only by a tiny bit if the data is taken to 2016).

You then suggested that ECS is a terrible metric and maybe TCR is preferable. It isn’t. One reason why, is because it is a linearised variable constrained by the rate that heat comes out of the ocean over time. Only then do you get the bulk of the positive feedback that is the uncertainty associated with how much the planet will warm (in terms of ‘fast’ sensitivity).

TCR and ECS might be model-derived, but they approximate real-world processes. Using models is the only way to unpack these processes.

ECS has more variation, therefore is better suited to untangling warming’s various influences. My view is the same as Held and Winton, that it cannot be narrowed much by working back from observed doubling. And because we are messing with ice albedo and other things, other factors affecting feedbacks are coming into play, so by the time you wait, there are new factors operating to mess with conclusions.

We need to understand risk based on the info we have, because in this area, it isn’t going to get much better.

“The IPCC refers to the TCR in an idealized experiment where only CO2 is changed, and where various rapid feedbacks are taken into account. *You* want to look at the temperature change after we’ve reached a doubling of CO2 in a non-idealized real-life situation where other forcings may contribute positive or negative during this time. Stuff like a reduced or increased solar intensity, big volcanic eruptions, increased or decreased particulate emissions into the higher parts of the atmosphere, etc.”

The TCR refers to stuff we can control like CO2 and ignores stuff we can’t. To derive it, we need to to as suggested, then adjust it for all that stuff we didn’t control. By ignoring all this stuff, we could assume it canceled itself out. But it says little about stuff in the future we can’t control.

So, as an actionable number, we have the TCR plus all that stuff we can’t control. And we need to use in most cases, the land’s response but better yet, the regional response. And I do want these things before spending money, I want to know what I am going to get in return?